The present invention relates to a sling and to its method of manufacture and, more particularly, to heavy-duty slings which are required to move loads of substantial weight.
Many industrial and commercial operations require the handling and transporting of loads. In many commercially-significant cases, such loads are of great weight. In order to move such loads from place to place, one generally selects a load-lifting device which corresponds in strength and size to the load to be moved.
It has been proposed to use slings in many different applications for moving loads such as heavy machinery. Generally speaking, slings are lengths of rope, cable, band, chain, belt or the like having bight-shaped end portions, also called loops or eyes. Such slings are versatile load-lifting devices and are easily adaptable to the particular size, contour and weight of the load to be moved.
It has been proposed to make a sling of a length of rope with bight portions formed by bending the ends of the rope into a loop shape and, thereupon, by attaching these ends to the main rope portion by sewing, braiding or tieing.
It has also been proposed to make a sling of a flat band with bight portions formed by bending the ends of the band into a loop shape and, thereupon, by attaching such ends to the main band by sewing or by stapling.
It has further been proposed to form slings of many turns of a flat band or of a belt and, thereupon, to interconnect the various juxtaposed turns by sewing therethrough with thread. However, such slings do not have a high load-lifting capability, because the thread stitches pass through the various juxtaposed turns. By piercing through the juxtaposed turns, the overall strength of the sling is actually weakened.
It has still further been proposed to form slings of flexible steel cable or similar metal material. In such cases, the bight-shaped end portions are formed by bending the ends of the cable and, thereupon, by attaching the cable ends to the main cable by means of clampable retaining rings. Although such slings are effective for their intended purpose, they have the serious disadvantage of mechanically damaging the load during lifting. It has been found that the steel cable and the metallic clamps actually mar and scratch the load to be moved, thereby substantially damaging the latter.
Another prior-art proposal utilizes metal links successively connected one after another in a manner similar to chains. These links may be small, or simple in construction, or large, or complex in construction. In any case, such slings have the decided disadvantage that they are only as strong as their weakest link.
Still another prior-art proposal utilizes a metal core covered at its exterior with an elastomeric substance. Such slings are not flexible so as to easily conform to the contour of a load to be moved. Furthermore, such slings are prone to frequent damage inasmuch as the elastomeric substance can be cut relatively easily by sharp metallic edges found on many loads to be moved.